1. Field of the Invention
The present invention pertains to indicators and more particularly to indicators that display the condition of the contents of containers where knowledge of the condition of the contents of the container is necessary for the performance of supporting activities.
2. Related Prior Art
In the area of material drying, such as sand drying, the relative moisture content of material to be dried must be known. The relative moisture content is often critical to the speed with which a subsequent dependent process may be accomplished. In some processes, such as drying sand, a high moisture content may prevent the drying process from being accomplished or completed efficiently or satisfactorily.
For example, in a sand drying plant where the sand is to be added to aggregates and oil derivatives to form asphalt, the moisture content of sand must be decreased to a predetermined level. Sand is scooped up from an outdoor pile and placed in a large tumbler. The sand is put through a drying procedure where hot gas is circulated over the wet sand, run through a dryer transition stage to a dust collector and then exhausted through the use of a large exhaust fan. The temperature of the exhaust is low when moisture is present in the sand and increases as the moisture content decreases or the sand is dried. When more sand having a significant moisture content is placed in the drying area, the temperature of the exhaust gas drops again, depending on the amount of moisture in the sand.
Although all the sand is taken from the same mound, in most cases taking sand from higher on the mound will result in loading sand with a lower moisture content. This is due primarily to the effect of gravity (moisture, i.e. water, is heavier than air and will tend to leach to the lower areas of the mound) and the drying effect of the sun and wind which will be most noticeable on the top and exposed sides of the mound. The drying effect of the sun and wind can be very rapid and significant and can aid in the drying process. In general, dropping the height of the bucket into which sand is loaded by a mere four inches, that is, taking the sand from deeper on the mound where it has a higher moisture content, can produce a significant change in the drying operation. The resulting change can be so significant that it can mean the difference between an efficient successful drying operation and one which operates too slowly and inefficiently, causing costs to increase because of increased man hours and increased gas consumption.
Unfortunately, the person who has the most control over the amount of moisture in the sand being loaded, and as a result, the gas consumption, has the least knowledge of the amount of moisture in that sand and the amount of gas being consumed. The dryer operator located in the control room is the only person who has the information concerning the moisture content through the knowledge of the amount of gas being consumed to dry the sand.
There are many types of moisture indicators in the art. Some detect the amount of moisture contained in a substance directly by insertion of a probe into the material, measure the moisture content and provide a digital readout of the actual moisture content. One such type is the xe2x80x9cAQUA-SPEARxe2x80x9d moisture meter manufactured Mastrad Company.
U.S. Pat. No. 4,047,105, titled xe2x80x9cMethod and Apparatus for Providing an Output Indication Proportional to the Moisture Content of Particulate Materialxe2x80x9d, issued to Bruce Olen Anderson relates to method and apparatus for providing an output indication proportional to the moisture content of particulate material where a probe drive signal having a predetermined frequency and amplitude is inserted and applied to the particulate material. A current indicator signal proportional to the current applied to the particulate material is provided. The current signal is proportional to the moisture content of the particulate material.
U.S. Pat. No. 4,621,229, titled xe2x80x9cInstrument for Measuring the Moisture Content of Solidsxe2x80x9d, issued to Friedrich Hirth, relates to an Instrument for measuring the moisture content of solids that has probes which are placed in contact with the material which is to have its moisture content measured. The probes are used to measure the electrical resistance of the material. A d.c. voltage is connected with the probes and generates the voltage required for measurement of electrical resistance. The characteristic line representing the electrical resistance of the material as a function of its moisture content is logarithmic in nature and, in order to generate a straight characteristic line, the signals from the probes are fed to a logarithmic amplifier. The amplified signals are converted to a moisture content which may be read from an indicator constituting part of the instrument. A calibrating unit is interposed between the logarithmic amplifier and the indicator and functions to adjust the characteristic line of the instrument so that this at least approximates the characteristic line of the material undergoing moisture determination.
Other types of moisture indicators may provide a reading by color change. Humidity Indicators manufactured by AGM Container Controls, Inc. are of this type. In general, these indicate the amount of humidity in a specific area. For example, this type of moisture indicator is placed in a closed area such as a room or section of a building. The ambient air humidity is indicated by the color of the indicator. When dealing with a large area such as a room, the color change will be slow to indicate a gradual change in humidity and not an instantaneous change for a small area.
The present invention provides a moisture indicator in an air flow drying process where hot gas is circulated over and around a granular material. Typically, this granular material has an undesirable amount of moisture content. In this process, the temperature of the gas after it has been circulated over the wet or damp sand provides an indication of the moisture content of the sand. The greater the moisture content in the sand, the cooler the exhaust gas and conversely, the dryer the sand, the hotter the exhaust gas temperature. The moisture indicator of the present invention includes a detector located in the path of the exhaust gas to determine exhaust flow temperature. A detector is placed in the gas flow process after it has been circulated over the sand to detect temperature of the exhaust gas. A valve control device is either electrically or mechanically associated with the temperature detector. This valve control device is used to control the flow percentage of hydrocarbon gas in the hot gas intake. When the temperature of the gas in the exhaust section drops below a predetermined level, a signal is sent to the valves that control the amount of flammable gas (hydrocarbon heating gas) in the intake flow. This signal causes the valves to open, increasing the percentage of heating gas in the gas flow, increasing the temperature of the hot gas intake. An indicator is connected or linked with the valve control device. The indicator is associated with a display showing the percent of hydrocarbon gas that is currently being fed to the hot gas intake in order to maintain a predetermined temperature in the exhaust gas. This in turn provides an indication of the amount of moisture in the granular material that has just been loaded into the moisture dryer. The percentage of hydrocarbon gas in the intake gas flow is directly proportional to the percentage of moisture in the granular material being dried. The indicator is operated in conjunction with the valve control for the intake hydrocarbon gas and is indicative of the amount of moisture in the granular material as a function of the percentage of gas needed to maintain a predetermined temperature in the exhaust gas. This provides a signal to the loader operator as to whether the granular material loaded has an acceptable amount of moisture for successful, efficient operation of the drying process or whether he should take sand or other granular material from another location.